Nine people have been hospitalized, with five in serious condition, following an accident at a seaside music festival in Vigo, Spain, on Sunday night. The boardwalk caved during the event’s closing ceremonies and fell into the sea, taking down several concertgoers into the water below, the New York Times reports.

The mayor of Vigo has launched an investigation into the incident, which resulted in a total of 313 injured guests, according to CBS News. Enrique Cesar Lopez Veiga, the president of the Vigo port authority, told Cadena Ser radio that he believes the pier most likely crumpled “because of excessive weight” as hundreds of people danced to live music atop the wooden panels.

The break occurred around midnight at the center of the pier, which stretched for about 130 feet. As the floorboards cracked and collapsed, attendees slid down the wood and into the water underneath. Through late Monday morning, rescue teams and divers searched through the wreckage for victims potentially stuck under the collapsed wood, but Galician authorities have reported no fatalities, according to the Times.

Typically a summer celebration, the annual Spanish festival includes live musical performances and sporting events. This year’s accident occurred during a set from Spanish rapper Rels B.